1. Technical Field
The invention relates to the field of electrochemical gas generators, and more particularly for an electrode composition and method for forming electrodes for ceramic oxygen generating systems (COGS).
2. Background Art
Electrochemical devices, such as fuel cells, oxygen sensors, and oxygen separation membranes are becoming increasingly popular as candidates for a variety of applications. Elevated operating temperatures required for efficient operation of these devices pose a major challenge for achieving required cost, power efficiency, and device longevity for prospective markets.
Common failure modes of the electrodes or current collectors in oxygen separation membrane systems include:
a. Densification of porous electrode and current collector coatings during operation;
b. Chemical attack of coatings by atmospheric contaminants; and,
c. Delamination of coatings from each other and from the substrate.
Typical current collectors which operate in an oxidizing atmosphere at temperatures exceeding 600° C. include Silver (Ag), Gold (Au), Platinum (Pt), Palladium (Pd), and alloys of these constituents. Although the combination of high electrical conductivity and low cost makes Silver (Ag) an attractive material, its tendency to sinter and vaporize under typical operating temperatures limits the applicability of the material in its pure form. Silver is also vulnerable to chemical attack in some conditions that might be encountered in the case of chemical warfare or other contaminated environments, as well as oxidation when in contact with high pressure, high purity oxygen. Inclusion of other precious metals, and their alloys, lead to a dramatic reduction in conductivity and increase in cost.
Examples of such known electrodes used with electrochemical gas generating systems are disclosed in U.S. Pat. No. 5,378,345, issued Jan. 3, 1995; U.S. Pat. No. 5,985,113, issued Nov. 16, 1999; U.S. Pat. No. 5,972,182, issued Oct. 26, 1999; U.S. Pat. No. 6,194,335, issued Feb. 27, 2001; U.S. Pat. No. 6,203,676, issued Mar. 20, 2001; and U.S. Pat. No. 6,290,757, issued Sep. 18, 2001.
Delamination between precious metal coatings and other coatings or substrates is common due to the relatively higher thermal expansion of the metal coating versus the other materials, typically ceramic, used in electrochemical devices.
The present invention includes an electrode and current collector system that is resistant to the aforementioned failure modes, while minimizing the use of precious metals, thereby enhancing overall electrochemical system performance and reducing cost as compared to traditional or known approaches.
While the above cited references introduce and disclose a number of noteworthy advances and technological improvements within the art, none completely fulfills the specific objectives achieved by this invention.